ML19340F176
| ML19340F176 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/16/1981 |
| From: | Phillips L Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19340F174 | List: |
| References | |
| NUDOCS 8101210225 | |
| Download: ML19340F176 (5) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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Metropolitan Edison Company
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Docket No. 50-289 (Three Mile Island Nuclear
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Station, Unit 1 Restart)
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NRC STAFF TESTIMONY OF LAURENCE E. PHILLIPS SUPPLEMENTARY TESTIMONY TO THAT OF LAURENCE E. PHILLIPS FILED DECEMBER 1, 1980 REGARDING REACTOR WATER LEVEL INSTRUMENTATION (UCS Contention 7, Sholly Contention 6(b) and ANGRY Contention 5(b))
Q.ls Metropolitan Edison in their October 2,1980 letter (TLL 500) to the NRC takes the position that no additional instruments are necessary or desirable since the NRC has not identified any needed improvements in the inadequate core cooling guidelines. Has tne staff responded to this position to make clear that additional instrumentation will be required?
A.
The position stated in the reference correspondence is no different than the position previously taken and addressed by the staff in the TMI-I Restart Evaluation, NUREG-0680, June, 1980, pp. C8-20 and 21.
Additionally, the present staff position, including rejection of the cited position of the licensee, is clearly stated in the September 24, 1980 letter and SER from D. Eisenhut to R. C. Arnold of Metropolitan Edison.
The staff requirements for Metropolitan Edison and all other licensees are further reinforced by the issuance of NUREG-0737 in 0101210Qg$
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- November, 1980. Metropolitan Edison, in their letter of November 20, 1980 (TLL 591), did acknowledge the staff requirements and promised to provide a response by January,1981.
The staff has provided no comment on the October 2 letter and will have nothing to add to the discussion and staff position already provided until we complete our review of the January submittal.
Q.2s Since the staff has not identified differences in operator actions if level inforwetion were available versus the actions that are prescribed by the existing Inadequate Core Cooling guidelines, what is the need for reactor vessel level indication?
A.
The Met Ed/B&W procedures for detection of Inadequate Core Cooling rely primarily on the saturation meter and core exit thermocouples.
The raturation meter, while providing a basis for initial actions, does not distinguish between anomalous transients which can drain the pressurizer and cause primary loop saturation due to cooling and shrinkage of primary coolant versus loss of coolant inventory which could lead to inadequate core cooling if it continues.
TMI-1 Emergency Procedure 1202-6B describes the different operator responses to snell break LOC' /ersus overcooling events which cause automatic high pressure injection. These procedures now require the operator to distinguish between the transients based on indirect indicators from existing instrumentation. Vessel level instrumenta-tion, if available, would permit a much quicker and more reliable diagnosis of the conditions.
For small break LOCA, an orderly cool-l l
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down is required, but not necessarily for an overcooling transient.
In both cases, a vessel level meter if available, would provide coordi-nating information to assist the operator in restoring the water solid
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primary system (possibly using the upper head vent) and the nornal water level in the pressurizer.
For a small break LOCA, the primary system will continue to lose coolant inventory, at a rate and duration dependent on the size and location of the break, until the safety injection make-up flow exceeds the rate of coolant loss. For some conditions, the time interval from the instant of primary system saturation conditions until the occurrence of superheat indication on the core exit thermocouples or hot leg RTDs is in excess of 30 minutes, and possibly up to three hours or more. The superheat condition does not occur until the core is partially uncovered and fuel heat up has begun.
If level instrumentation were available, the effectiveness of HPI in recovering the system and the trend of level indication (continuing to lose coolant or refilling the system) would provide valuable diagnostic information on the nature of the transient before the level drops into the core.
The level indication would also provide evidence that the core is covered during recovery from a TMI-2 type flow blockage condition, even though superheat may persist at the core exit thermocouples.
None of the process parameters monitored by existing instrumentation provide equivalent information on a continuous basis.
- '4 The NRC staff has not evaluated the possible actions the operator would take based on core level instrumentation but has required that the-licensees describe how emergency procedures should be modified after level instrumentation is incorporated (Item (7) and (8) of Documentation Required in II.F.2 of NUREG-0737). Met Ed has not yet submitted any analyses or evaluation addressing additional operator actions which could be taken to prevent core uncovery for small break LOCAs if level information were available for prompt diagnosis of the condition.
A recent event at St. Lucie (June 11,1980) provides a classic example of an anomalous event leading to steam bubble formation in the reactor vessel head. The condition was not recognized by plant operators since instrumentation was not available to detect the low-level condition. The post-event evaluation concluded that unsafe operator actions could have been taken.
("ReportontheSt.Iacie I Natural Circulation Cooldown on June 11, 1980," by E. V. Imbro, Offict for Analysis and Evaluation of Operational Data, USNRC.) Vessel level information would have indicated the void formation in the upper head and thus prevented operator confusion which contributes to the likelinood of unsafe actions. Additionally, vessel level indication would provide a safe bases for manual shut off of HPI to a'/oid overflow i
to containment.
Finally, vessel level information is important and possibly essential to proper emergency procedures relating to use of the reactor vessel l
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head vent required by the TMI Action Plan. Vessel level information would indicate the existence of a void in the upper head so that the need for vessel venting could be evaluated.
The NRC staff has not evaluated the conditions for which the head vent should be opened and has requested that procedures for use of the vent be provided by the licensee. However, the staff is aware of at least one vent design for which the designer insists on the coupling of level infotmation to the safe operation of the vent.
In summary, the staff believes that reactor vessel level information will enhance the operating safety of PWRs.
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